![]() ![]() In situations where these light waves meet and interact, they can either become more amplified or cancel each other out. As light encounters an edge, it is bent and redirected, sending it in different directions. The second section is headlined “How Does Diffraction Happen?” Underneath this headline is a caption that says, “Light, which has wave-like properties, tends to radiate from a central point outward, similar to how water behaves when a stone is tossed into it. For most reflecting telescopes, including Webb, diffraction spikes appear when light interacts with the primary mirror and struts that support the secondary mirror.” Below this is an image of Webb’s observing side, including its 18 gold hexagonal segments, science instruments, primary mirror, struts and secondary mirror. While all stars can create these patterns, we only see spikes with the brightest stars when a telescope takes an image. Diffraction spikes are patterns produced as light bends around the sharp edges of a telescope. The first section is headlined “What Are Diffraction Spikes?” Below the headline is a caption that says, “Have you ever noticed that bright stars in your favorite space images have unique spikes around them? These are known as diffraction spikes. This diagram is composed of five sections. The top right of the image shows three stars producing eight-pronged diffraction spike patterns. That’s expected to happen early this summer.This is a diagram labeled “Webb’s Diffraction Spikes”. That will likely take many weeks, and then, after that, a final pass-through is done to make final corrections to the submirror pointings.Īnd then, and then, the gigantic observatory will be open for scientific business. And then this has to be done on the other JWST instruments: the Fine Guidance Sensors, the Near Infrared Spectrograph, and the Mid-Infrared Instrument. The next step is to make sure they can do this in different spots on the detector, so that everything in the field of view is as well focused as possible. All 18 mirrors are now able to send light to a single spot on the camera. This image shows the results.īut we’re nowhere near done. Over the past few weeks, the mirrors have been painstakingly adjusted, first in a course phasing and now fine phasing, so that they all act together. This is what’s being used to “see” the photons of light from the mirrors. In fact, the workhorse instrument on JWST is the Near Infrared Camera, or NIRCam. All 18 submirrors have to be incredibly well aligned, acting together to see the same object at the same time and focus its light as accurately as possible on the same spot on a detector. What does that mean? The primary mirror of JWST is actually composed of 18 smaller hexagonal mirrors about 1.3 meters in size, arranged in a bigger hexagon that’s about 6.5 meters across. It’s a calibration image, taken in a single color, meant to test the ‘scope’s abilities and not analyze the objects in it for science. There are also many very faint stars in the image as well.īear in mind this is not a science image. Another friend and astronomer, Grant Tremblay, found the brightish galaxy on the left in a database it’s probably over 3 billion light years away!įrom the ground, the star is so bright it swamps faint nearby objects, but JWST’s keen vision even now can separate them. These spikes are a little irritating scientifically, since bright spikes can obscure objects you might want to see, but they’re pretty.īut even cooler, you can see lots of other objects in the image! Several dozen background galaxies are scattered throughout the field of view, nearly all of which are too faint to have been clearly seen before. ![]() The horizontal line is an actual support structure diffraction spike, which makes sense to me: The light brightens and dims along the line, which is caused by constructive and destructive interference in the light, and that’s typical in that kind of spike.There are two other support structures, but they align with the edges of the hexagonal submirrors, so their spikes are mixed with the mirror edge spikes. ![]() So the six edges of the mirrors are what cause the diffraction. The horizontal line is due to the top strut the two lower struts align with mirror segment edges, so don't add an extra pattern. About the spikes (the "Point Spread Function" PSF): diffraction due to the hexagonal mirror segments causes the 6 big spikes. ![]()
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